Method of die casting



Sept. 6, 1966 H. D. HALL ETAL 3,270,383

METHOD oF DIE CASTING Filed June 24, 1963 2 Sheets-Sheet l WVENTORS ATIURNEV/ Sept-6, 1966 H. D. HALL ErAL METHOD 0F DIE CASTING 2Sheets-Sheet 2 Filed June 24, 1963 United States Patent O 3,270,383METHOD F DIE CASTING Harry D. Hall, Birmingham, David C. Salatin, RoyalOak, Don R. Sutherland, Mount Clemens, and Clayton J. Trible, Berkley,Mich., assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Filed .lune 24, 1963, Ser. No. 289,903 Claims.(Cl. 22-200) This invention relates to die casting and more particularlyto a process -for making improved die castings and to apparatus forcarrying out the process.

Conventional die casting procedures involve injecting molten metal intoa die cavity at a relatively high pressure in order of 10,000 pounds persquare inch by means of a piston-like ram. Typically, the molten metalis forced through a restrictive sprue passage to cause the metal toenter the die cavity in particulate for-m and at a high velocity tofacilitate filling of the die cavity. The molten vmetal therefore entersthe die cavity in a highly turbulent state and the high pressure of theinjection is relied on to compress the molten metal in the die cavity toobtain reasonably dense castings. Die casting procedures of this typemay be of the hot-chamber type, as is typically used in zinc diecasting, in which the injection mechanism or gooseneck is submerged in amass of molten metal or of the cold-chamber type, typically used inaluminum or magnesium casting, in which the injection mechanism ismaintained in an atmospheric environment. The principal advantage in theabove high pressure type of die casting is in the speed with which thecastings are made since only a few seconds are involved in the entireprocedure of injecting the molten metal-into the die cavity,solidification of the casting, and its removal from the die. Theprincipal disadvantage of this high pressure type die casting is thatsince as above indicated the metal is injected into the dies under highpressures rand generally through a res-tricted sprue opening the metalenters the 'die cavity in a highly turbulent condition with the resultthat the castings tend to be porous and unsuitable for many purposes.Thus, for example, castings made by the above-)mentioned high pressuredie casting are suitable for automotive body hardware, ornamental parts,and the like. However, due to the inherent porosity of such castings,they are generally unsuitable for making cylinder blocks, cylinderheads, pump housings, and the like.

Another well-known type of die casting generally referred to as lowpressure casting involves mounting the dies over Van enclose-d pot ofmolten metal, providing a tube or stalk which extends 'from a pointwithin the molten metal to the sprue of the die, and subjecting themolten metal to a superimposed pressure differential in the order of afew pounds per square inch whereby the molten metal is forced slowly upinto the stalk and thence into the die cavity under essen-tiallynon-turbulent conditions. The principal advantage in this type of diecasting is that a more dense casting is formed. The principaldisadvantage resides in the fact that a typical casting cycle req-uiresa considerable amount of time since the molten metal is injected intothe die cavity slowly and slow solidification is provided to preventpremature solidification of the casting in the cavity.

It is the principal object of this invention to provide an improved diecasting process whereby highly improved, dense castings are made 4at arelatively high speed and whereby the advantages of prior :artprocedures are realized and the disadvantages are eliminated. Anotherobject of this invention is -to provide apparatus 4for carrying out thisprocess These and other objects are carried out by apparatus ,27(l,383vPatented Sept. 6, 1966 ice generally of the cold-chamber type having anovel cornbination of machine elements including an enlarged gate ofsuicient volume to permit non-turbulent passage of the molten metaltherethrough into the die cavity, a coldcharnber type shot sleeve, aduplex shot plunger operable within the shot sleeve consisting of arelatively small diameter plunger reciprocally operable within a largerdiameter plunger of substantially the same 'diameter las the shotsleeve, wherein the tip of the smaller plunger is adapted to bepositioned substantially at the tip of the larger plunger in a firstposition thereof and to extend to a longitudinal position substantiallybeyond the tip of the larger plunger in a second position thereof, andhydraulic and control means for operating the two plungers as a unitwhen the plungers are in said first position and for operating thesmaller plunger independently of the larger one to obtain said secondposition.

The process includes the steps of admitting a measured charge of moltenmetal into the shot sleeve, operating the duplex plunger as a unit tomove the molten metal non-turbulently into the die cavity in the form ofa solid front, maintaining a relatively high compacting pressure on themolten metal by means of the duplex unit until a realtively thin shellof molten metal has solidified adjacent the walls of the `die cavity,the gating, and the duplex plunger tip to prevent further application ofcompacting pressure and thereafter actuating the smaller plungerindependently of the larger one whereby its tip breaks through thesolidified metal shell adjacent the tip orf the smaller plunger tothereby subject the molten core portion of the metal in the die cavityto continued high pressure and continued filling until'the metal hassolidified.

Preferably, means are provided whereby the actuation of the smallerplunger is in response to the pressure built up against the largerplunger due to the aforementioned solidified metal shell having beenformed adjacent the plunger and shot sleeve walls thereby preventing thelarger plunger from subjecting the molten metal in the die cavity -tofurther compression and whereby the solidilication of the casting is notpermitted to progress to a point which would involve solidification ofthe core portion of the casting or to a point which would make itdifficult for the smaller plunger to break through the solidified shell.

Other objects and advantages will be apparent from the followingdetailed description of the invention, reference being had to the-accompanying drawings of which:

FIGURE 1 is a fragmentary cross-sectional view of die casting apparatusembodying this invention showing the dies and injection mechanism in aposition just as the die cavity is filled with molten metal.

FIGURE 2 is a fragmentary cross-sectional view of the die cavity andplunger tip portion of the apparatus at an intermediate stage of theprocess of this invention just prior to the actuation of the smallerplunger.

FIGURE 3 is a fragmentary cross-sectional view similar to that of FIGURE1 but after the actuation of the smaller plunger.

FIGURE 4 is a view of the apparatus shown in FIG- URE l together withhydraulic and electrical control apparatus shown in schematic form.

Referring now to the drawings and particularly to FIGURE 1, it will beobserved that there is included in the fragmentary illustration of thedie casting machine a cover die 10 and an injector die 12 defining a diecavity 14 therebetween. The die member 10 is supported on the face of astationary platen 16 by suitable bolts (not shown) which in turn ismounted on a base plate (not shown).

The stationary platen 16 also supports one end of each of fourlongitudinally extending tie bars 18, the opposite end of each of thetie bars being supported by a suitable upright stationary plate (notshown).

The movable ejector die 12 is supported on the movable platen 20`mounted on the tie rods 18 for longitudinal movement thereon. Themovable platen 2() is movable reciprocally along the tie rods 18 betweendie open and closed positions by means of a toggle device 21 as is wellknown in the art.

In the space within the movable die 12, there is provided an ejectingmechanism comprising a head plate 22 and a plurality of ejecting pins24. rThe ejecting pins 24 are each secured at one end of the head plate22 and are slidably received in suitable bores formed in the ejector die12. A plunger 26 has its forward end secured to the head plate 22 of theejecting mechanism and extends rearwardly through an axially alignedbore in the die 12 and the movable platen 20. A bushing 28 havingsealing rings 30 is provided to prevent leakage through the movableplaten about the plunger 26. When the movable platen 20 is retracted andclosely approaches the limits of its rearward movement, the plunger 26is adapted to engage a stop (not shown) whereby its rearward movement isterminated. The continued movement of the platen to its rearward limitthereafter results in relative movement between the platen 20 and theplunger 26 and between the ejector pins 24 and the movable die 12, thefront ends of the pins being urged outwardly from the face of the die todislodge the casting formed in the cavity.

Extending snugly through the aligned bores in the platen 16 and thecover die 10` is a shot sleeve 32 having a vertical extending opening 34therein for admitting a charge of the molten metal into the shot sleevein any well-known manner. An important aspect of the invention residesin the provision of a wide gating 36 extending from the end of the shotsleeve 32 into the die cavity proper 14. As will hereinafter more fullybe described, the gating 36 is of sutiicient volume so that the moltenmetalmay be moved into the die cavity 14 without significant turbulence.As may be seen from the drawing, the gating 36 may be initially of thesame dimensions as the shot sleeve to avoid turbulence as the moltenmetal changes from horizontal to vertical flow into the die cavity.

Another important aspect of the invention resides in a duplex plungerindicated generally as 38 which consists of a relatively larger outerplunger 40 snugly and reciprocally received in the shot sleeve 32 and arelatively small plunger 42 reciprocally received within a longitudinalbore of the larger plunger 40' centrally thereof. The larger plunger 40is slidably supported on a plurality of tie rods 44, each bolted 'at oneend thereof to the station ary planten 16, 'by means of the flange 45integrally attached to the plunger 40. To the opposite ends of the tierods 44, there is bolted a hydraulic cylinder 46 including a piston stop47 attached to the end thereof and having a piston 48 reciprocallypositioned therein. The piston 48 is attached to` a connecting rod 50which is slidably mounted on the tie rods 44 by means of the integralange 52. .The flange 52 is connected to the flange 45 of the plunger 40`by means of the cylinder 54 welded thereto whereby the piston 48 isconnected to the plunger 40 by means of the connecting rod 50, theflanges 45 and 52, and the cylinder 54. The anges 45 and 52 have alignedbores 4therein which receive the bushings 56 and are welded thereto.These in turn slidably receive the tie rods 44. The cylinder 54 alsoforms a hydraulic cylinder including the piston stop 55 attached to therod 50, which contains a piston 58 attached to the smaller plungerpiston 42.

It will thus be observed that reciprocal motion of the piston 48 isoperable to move the smaller or inner plunger 42 and the larger or outerplunger 40 as a unit. On the other hand, the reciprocal motion of thepiston 58 is operative to reciprocate the inner plunger 42 independentlyof the motion of `the outer plunger 40. As will be hereinafterdescribed, hydraulic and control means are provided for moving the outerplunger 40 Aand the inner plunger 42 in a predetermined sequence inaccordance to the requirements of the process of this invention.

Referring to FIGURE 4 an example of suitable hydraulic mechanism forpracticing the process of this invention includes a gear pump 62 havingan input line 64 connected to an oil sump 66 and an output line 68connected to a relief valve 69 discharging to the sump; to anaccumulator 70; to a first line 72 connected to the portion of thecylinder 46 -outwardly of the piston 48 through a flow control valve 73,a two-way solenoid operated valve 76, the hydraulic line 79 and thehydraulic line 84; and to a second line 78 connected to the portion ofthe cylinder 46 outwardly -of the piston 48 through the flow controlvalve 80,' the solenoid operated four-way valve 82 and the lines 77 and84. The line 78 is also connected to that portion of the cylinder 46inwardly of the piston 48 through the ilow control valve 80, thefour-way solenoid operated valve 82 and the line 83. The outlet 68 ofthe gear pump 62 is also connected to a third line 86 which connectswith the portion of the cylinder 54 outwardly of the piston 58 throughthe fourway solenoid operated valve 88 and the reducing valve 98. Theline 86 is also connected to the portion of the cylinder 54 inwardly ofthe piston S8 through the lfourway valve 88 and the line 89. The portionof the cylinder 46 inward -of the piston 48 is also connected to the oilsump 66 through the line 83, the four-way valve 82, and the line 81.'I'he portion of the cylinder 46 outward of the piston 48 is alsoconnected to the oil sump through line 84, the four-way valve 82 and theline 81. Similarly, the` portion of the cylinder 54 inw-ard of thepiston 58 is connected to the oil sump 66 by means of the line 89, thefour-way valve 88, and the line 87; and the portion of the cylinder 54outwardly of the piston 58 is connected fto the sump 66 through the line92, the four-way valve 88 and the line 87. The lcharacter and operationof the electrical components for operating the hydraulic apparatus willbe apparent from FIGURE 4 and the detailed description' of the operationof the mechanism to -be made hereinafter.

The process of this invention stated generally in terms of FIGURES l, 2,and 3 involves rst returning the duplex plunger 38 to a cyclecommencement position in which the plunger 40 is withdrawn sulcientlyfrom the shot sleeve to expose the inlet 34. When operated as a unit thetips of each of the plungers are substantially aligned to form acomposite tip of more or less conventional shape. A measure charge ofthe molten metal is poured into the shot sleeve which is suicient tolill the die cavity 14 as well as the enlarged gating portion 36 whenthe plunger 38 reaches the end of its stroke. Hydraulic fluid is thencaused to enter the hydraulic cylinder 46 on the side thereof outward ofthe piston 48 whereby the duplex plunger 38 including the outer plunger40 and the inner plunger 42 moves as a unit forward toward the diecavity to nonturbulently move the molten metal into the die cavity 14.The volume of the gating 36 and the speed of the duplex plunger is suchas to provide a lineal velocity through the gate not in excess of about50 feet per second, i.e., a nonturbulent flow, whereby a solid front ofthe metal moves into and fills the cavity. Just before the die cavity 14is filled with molten metal, additional hydraulic pressure is ,appliedoutwardly of the piston 48 where'by a squeeze in the neighborhood of5,00()-l0,000 pounds per square inch is applied to the metal in the diecavity 14. The molten metal begins immediately to solidify in the diecavity and the gating adjacent the metal walls of the die. After thelapse of a short period of time in the vicinity of a fraction of asecond, a relatively thin layer of the molten metal 124 is formedadjacent the metal walls of the die within the die cavity 14 as well asthe gating 36 and over the tip .of the duplex plunger as shown in FIGURE2. The formation of this metal shell prevents the further application ofpressure by the duplex plunger tip on the molten metal sin-ce this metalshell creates an annular barrier 126 about the periphery of the duplexplunger tip. This condition is evidenced by a marked increase in thehydraulic pressure developed in the cylinder 46 outwardly of the piston48. Electrical and hydraulic control mechanism is provided to cause thisincrease in pressure to then admit hydraulic pressure into the cylinder54 outwardly of the smaller piston 58 whereby the smaller inner plunger42 is caused to move forward and break through the shell 124 as shown inFIGURE 3 and whereby the core or internal molten portions of the castingis subjected to continued pressure 4on the order of 10,000 pounds persquare inch to further feed molten metal into the die cavity tocompensate for shrinkage until the molten metal has solidified, andthereby produce a high quality dense casting. After the metal hassolidified, the hydraulic pressure outwardly of the smaller piston 58 isrelieved and hydraulic pressure is applied to the cylinder 54 inwardlyof the piston 58 whereby the smaller plunger 42 is withdrawn from thecasting. The dies are then opened and the continued pressure of theduplex plunger upon the solidified gating biscuit forces the latter fromthe cover die 10. Thereafter the pressure in the cylinder 46 outwardlyof the piston 48 is relieved and hydraulic pressure is applied inwardlyof the piston 48 whereby the entire duplex plunger is withdrawn from theshot sleeve so as to expose the inlet 34 preparatory to another castingcycle. Withdrawal of the smaller plunger 42 prior to the withdrawal ofthe larger plunger 40 is essential to efficiently eject the casting.

It will be apparent that the process described has a number of importantadvantages. As described above, the molten metal is moved into the diecavity slowly and non-turbulently in the form of a substantially solidfront so that atmospheric air in the die cavity is expelled through thedie vents ahead of the rising front of molten metal thus minimizi-ngcasting porosity due to air entrapment. The slow progressive filling ofthe die cavity operates to seal the die vents and the die parting linecrevices at low pressure and thus hashing (liquid metal escaping fromthe die cavity through the parting line and vents) is minimized. Thus,the process is particularly advantageous in producing castings with dieswhich are somewhat deteriorated lat the parting lines. Further, thesolid shell 124 is formed substantially at lower pressures and the shellfunctions to contain the molten metal within the shell when the highpressure is applied by the nal squeeze of the larger plunger and thesmaller plunger thus reducing the necessary die clamping force by asmuch as 50%. Moreover, the high pressures applied by the smaller plungercauses the shell 124 to lie up snugly against the casting cavity toobtain improved casting dimensions. A very important aspect of theprocess is that the inner portions of the casting are subject tocontinued pressure until complete solidication has been substantiallycompleted whereby shrinkage and porosity of the casting is minimized.

The process described may be advantageously practiced using thehydraulic and electrical apparatus shown in FIGURE 4. At thecommencement of a casting cycle, the dies and 12 have been closed byactuation of the toggle mechanism 21 operated by the usual hydraulicmeans and the duplex plunger 38 has Ibeen moved outwardly so that theplunger exposes the shot sleeve opening 34. The shot sleeve is thencharged with molten metal. At this time, t-he operator moves the switch96 to the plunger forward position shown in FIGURE 4. In this positionof the switch the contact 118 is open whereby the large plunger return4solenoid 119 of the four-way double solenoid valve 82 is deenergizedwhereby the portion of the cylinder 46 inwardly of the piston 48 is opento the oil sump 66 through the hydraulic lines 83 and 81. The contact102 thereof is closed to prepare the circuit of the solenoid 106 of thetwo-way valve 76. The contact 94 thereof is closed and is operative toenergize the forward motion solenoid 98 of the four-way valve 82 to openthe portion of the cylinder 46 outwardly of the piston 48 to hydraulicpressure from the gear pump 62 through the hydraulic line 78, the flowcontrol valve 80, and the lines 77 and 84. The closure of the contact 94also energizes the timer 99 to close the normally open contacts 101 and103 by means of the coil 100 and as will be seen is necessary at asubsequent stage of the cycle to return the smaller plunger 42 from itsforward position.

Actuation of the solenoid 98 causes hydraulic pressure to be admittedinto the cylinder 46 through the lines 77 and 84 whereby the duplexplunger moves relatively slowly into the shot sleeve as a unit movingthe molten metal Iahead of its non-turbulently and with a solid front.The flow of hydraulic fluid is controlled by the ow control valve toinsure a solid till flow Velocity of about 50 lineal feet per second Orless. As the duplex plungers nears the end of its stroke, it closes thelimit switch 104 by the action -of the cam 105 attached to the flange 52acting on the switch arm 107. The actuation of the limit switch 104energizes the solenoid 106 of the two-way valve 76 whereby the valveopens and additional hydraulic fluid with the aid of the accumulator 70is m-oved into the cylinder 76 outwardly of the piston 48 through thelines 72, 79, and 84. This increases the speed of the duplex plunger atthe very end -of its stroke and subjects the metal in the cavity to anincreased filling velocity. Since the gating is now submerged, the solidfront fill is not disturbed by this increased velocity and the resultinghigher pressure.

When the pressure in the cylinder 46 outwardly of the piston 84 buildsup to pre-set relatively higher pressure due to the die cavity havingbeen lled and the molten metal therein having been compressed, thepressure switch 108, which is exposed to the pressure in the outwardportion of the cylinder 46 through the Iline 85, is closed whereby thetimer 110, including the coil 112 and the contact 113, is energized toclose the contact 113. When the timer times out, which involves va timedelay in the neighborhood of a fraction of a second, sucient to allowthe solidification of the layer 124 and 126, the timer energizes thesolenoid 114 of the four-way valve 88 through the timer 99 which asdescribed above had been closed when the timer 99 was energized. As aconsequence, the portion of the cylinder 54 outward of the piston 58 issubjected to hydraulic pressure through the pressure `reducing valve 90,the line 92, the valve 88 .and the line 86 and the smaller plunger 42 iscaused to move forward and break through the solidied shell 124 as shownin FIGURE 3 to subject the molten material to continued pressure and tocause the shell to lie up snugly against the cavity walls and tocompensate for metal shrinkage.

A short time before the dies 10 and 12 are to be opened, the timer 99times out thereby de-energizing the solenoid 114 and energizing thesolenoid 116 of the four-way valve 88. This causes the hydraulicpressure outwardly of the piston 58 to be relieved through the lines 92and 87 and for hydraulic pressure to be applied inwardly of the piston58 through the lines 86 and 89. As a result, the plunger 42 is caused tobe withdrawn from the solidified casting biscuit and returned to itsoriginal position las shown in FIGURE 4. Thereafter, other mechanism isactuated (not shown) to open the dies and effect ejection of the castingby the action of the ejector pins 24 associated with the bar 22 andplunger 26 in a well-known manner. While the dies are being opened,however, continued pressure applied by the duplex plunger forces thecasting biscuit 127 (FIGURE 3) from the cover die.

After the dies are .fully open, the operatormoves the switch 96 to areturn position. As a consequence, the contact 94 is openedde-en-er-gizing the solenoid 98 and the timer 99. As a result, thehydraulic pressure outwardly of the large hydraulic piston 48 isrelieved. The contact 102 is opened de-energizing the solenoid 106 andthe contact 118 is closed energizing the return solenoid 119 wherebyhyd-raulic pressu-re is applied inwardly of the piston 48 through thelines '78 and 83 to return the duplex piston to its original position.The return of the piston 48 to its original position causes `the limitswitch 10d to open whereby the cycle is completed.

It will be understood that the control mechanism described above toillustr-ate the invention is a simplified version of control apparatuswhich may be used. However, it will be obvious to those skilled in theart that it is desirable to integrate the operation of the apparatusdescribed with the control of the ope-ration of the entire die castingapparatus and to install additional control and safety features.

Although the invention has been described in terms of a specificembodiment, it will be understood that various modications may be madewithin the scope of the invention.

We claim:

1. The method of die casting comprising the steps of moving by means ofa plunger a molten metal mass into the cavity of die casting diesthrough a substantially nonrestricted passa-ge at a velocity such thatya substantially solid front of the molten metal enters the die cavity,maintaining pressure on the molten metal by means of said plunger untilsubstantially only a layer of the metal has solidified 4adjacent thesaid die cavity and passage walls to arrest the further application ofpressure on the molten portions of the meal mass by said plunger, andthen forcing a second plunger through said layer and into the molteninterior portion of the metal mass to maintain pressure on the moltenportions of the mass until it has solidified.

2. The method of die casting comprising the steps of moving a mass ofmolten metal into the cavity of die casting dies through a substantiallynon-restricted passage by means of a plunger comprising a larger plungerhaving a smaller plunger reciprocal therein at a velocity such that asubstantially solid front of the molten metal enters the die cavity,maintaining pressure on the molten metal by means of said plunger untilsubstantially only a layer of the metal has solidified adjacent the diecavity and said passage walls to arrest the further application ofpressure on the molten portions of the metal mass, and then forcing saidsmaller plunger through said layer into the molten interior portion ofthe metal mass to maintain pressure on said interior molten portionuntil it has solidified.

3. The method of die casting comprising the steps of moving by means ofa first hydraulic means operated plunger a molten metal mass into thecavity of die casting dies through a substantially non-resistrictedpassage by a velocity such that a substantially solid front of themolten metal enters the die cavity, maintaining pressure on the moltenmetal by means of said plunger until substantially `only a layer of themetal has solidified adjacent said die cavity and passage walls toarrest the further application of pressure on the molten portions of themetal mass by said plunger, and then forcing a second plunger operatedby a second hydraulic means in response to the pressure build-up in saidfirst hydraulic means due to the formation of said layer into the molteninterior portions of the metal mass to maintain pressure on the moltenportions of the mass until it has solidified.

4. The method of die casting comprising the steps of moving a mass ofmolten metal into the cavity of die casting dies through a substantiallynon-restricted passage by means of a plunger comprising a larger plungerhaving a smaller plunger reciprocal therein and .adapted to form aportion of the tip of the larger plunger when in a first position and toextend substantially beyond the tip of the larger plunger when in asecond position at a velocity such that a substantially solid front ofthe molten metal enters the die cavity, maintaining pressure on themolten metal by means of said plunger until substantially only a layerof the metal has solidified adjacent the die cavity and said passagewalls to arrest the further application of pressure on the moltenportions of the metal mass, and then forcing said smaller plungerthrough said layer to said second position and into the molten interiorportion of the metal mass to maintain pressure on said interior moltenportion until it has solidified.

5. The method of die casting comprising the steps of moving by means ofa plunger a molten metal mass into the die cavity of die Casting diesthrough a substantially non-restricted passage in the form of asubstantially solid front, said molten metal filling the die cavityprogressively and filling and freezing in the vents and parting linecrevices at it fills the die cavity, then applying a relatively highpressure by means of said plunger substantially .at the time the diecavity is filled, maintaining said relatively high pressure on themolten metal by means of said plunger until a layer of molten metal hasformed adjacent the passage walls to arrest the application of continuedpressure on Ithe molten interior portions of the metal mass by saidplunger, and then forcing a second plunger into the molten interior ofsaid mass to maintain pressure on the molten portions of the mass andcontinued .feed of the die cavity until complete solidification hasoccurred.

6. The method of die casting comprising the steps of moving at arelatively low velocity by means of a plunger a molten metal mass intothe die cavity of die .casting dies through a substantiallynon-restricted passage lin the form of a solid front, said molten metal`at said low velocity filling the die cavity progressively :and fillingand freezing in the vents and parting line crevices as it fills the diecavity, then increasing the velocity of said plunger substantially atthe time the die cavity is filled to subject the molten metal to arelatively high pressure, maintaining said relatively high pressure onthe molten metal by mea-ns of said plunger until a layer of molten metalhas formed adjacent the passage walls to arrest the further applicationof continued pressure on the outer portions of the molten mass by saidplunger and then forcing a second plunger into the molten interior ofsaid mass to maintain pressure on the molten portions of the mass andcontinued feed of the die -cavity until complete solidification hastaken place.

7. The method of claim l wherein said second plunger is withdrawn fromthe casting before the dies are opened and pressure is maintained on thesolidified casting by said plunger after Ithe dies are opened to forcethe portion of the casting within said passage therefrom as the dies areopened.

8. The method of claim 2 wherein the smaller plunger is withdrawn fromthe casting before the dies are opened and pressure is maintained on thesolidied casting by said larger plunger after Ithe dies are opened toforce the portions of the casting within said passage therefrom as thedies .are opened.

9. The method of die casting comprising the steps of moving a mass ofmolten metal into the die cavity of die casting dies through asubstantially non-restricted passage by means of .a plunger comprising a`first larger plunger having a smaller plunger reciprocal therein ,andadapted to form a portion of the tip of the larger plunger when in afirst position and to extend substantially beyond -the tip of the largerplunger when in a second position,

said molten metal filling the die cavity progressively and filling andfreezing in the vents and parting line crevices as it fills the diecavity, then increasing the velocity of said larger plunger while saidsmaller plunger is in said first position to impose a relatively highpressure on the molten metal and to insure complete filling of thecavity substantially at the time the die cavity is filled, maintainingsaid relatively high pressure on the molten metal by means of saidplungers until a layer of solidified metal has formed adjacent saidpassage walls to arrest the application of continued pressure on themolten metal portions of the metal mass, and then moving said .smallerplunger to said second position thereby forcing said smaller plungerinto the molten interior of said mass to maintain continued pressure onthe molten portions of the mass and continued feed of the die cavityuntil solidification 'has occurred.

10. The method of die casting comprising the steps of moving a mass ofmolten metal into a die cavity of die casting dies through substantiallynon-restricted pas-sage by means of a plunger comprising a first largerplunger -operated by hydraulic means having a smaller plunger operatedby a second hydraulic means reciprocal therein and adapted to form aportion of the tip of the langer plunger when in a rst position and toextend substantially Ibeyond `the tip of the larger plunger when in asecond position, said molten metal filling the die cavity progressivelyand flling and freezing in the vents and the parting line crevices as itllsthe die cavity, then increasing the velocity of said larger plungerWhile said smaller plunger is in said rst position Ito impose therelatively high pressure on the molten metal and to insure completefilling of the cavity substantially at the time the die cavity is -lled,maintaining said relatively high pressure on the molten metal by meansof said plunger until a layer of molten metal has formed adjacent saidpassage walls to arrest the application of continued pressure on themolten metal portions of the metal mass, and then moving said smallerplunger in response to the pressure build-up in said rst hydraulic meansdue t0 the formation of said layer to said second position therebyforcing said smaller plunger by said second hydraulic means into themolten interior of said mass to maintain continued pressure on themolten portions of said mass and continued feed of the die cavity untilsolidication has occurred.

References Cited by the Examiner UNITED STATES PATENTS 2,581,550 1/1952Misfeldt 18-30 FOREIGN PATENTS 126,544 1/ 1948 Australia.

J. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 D 3,270,383 September 6, 1966 Harry D. Hall et al.

It :Ls hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 5l, for "planten" read platen column 6, line 16, for"plungers" read plunger line 3l, for "up to" read up to a column 7, line28, for "meal" read metal line 5l, for "non-resistrcted" readnonrestrcted Column 8, line 13, for "at" read as Signed and sealed this22nd day of August l96'7 (SEAL Atst:

ERNEST W. SWIDER EDWARD I. BRENNER Attest'mg Officer Commissioner ofPatents

1. THE METHOD OF DIE CASTING COMPRISING THE STEPS OF MOVING THE MEANS OFA PLUNGER A MOLTEN METAL MASS INTO THE CAVITY OF DIE CASTING DIESTHROUGH A SUBSTANTIALLY NONRESTRICTED PASSAGE AT A VELOCITY SUCH THAT ASUBSTANTIALLY SOLID FRONT OF THE MOLTEN METAL ENTERS THE DIE CAVITY,MAINTAINING PRESSURE ON THE MOLTEN METAL BY MEANS OF SAID PLUNGER UNTILSUBSTANTIALLY ONLY A LAYER OF THE METAL HAS SOLIDIFIED ADJACENT THE SAIDDIE CAVITY AND PASSAGE WALLS TO ARREST THE FURTHER APPLICATION OFPRESSURE ON THE MOLTEN PORTIONS OF THE METAL MASS BY SAID PLUNGER, AND